Non-volatile memory devices are currently in widespread use in electronic components that require the retention of information when electrical power is terminated. Non-volatile memory devices include read-only-memory (ROM), programmable-read-only memory (PROM), erasable-programmable-read-only-memory (EPROM), and electrically-erasable-programmable-read-only-memory (EEPROM) devices. EEPROM devices differ from other non-volatile memory devices in that they can be electrically programmed and erased. Flash memory devices are similar to EEPROM devices in that memory cells can be programmed and erased electrically. However, flash memory devices enable the erasing of all memory cells in the device using a single current pulse.
A flash memory device typically includes a core region and a periphery region. The core region includes memory transistors, while the periphery region contains both low-voltage transistors for handling logic and switching circuitry, and high-voltage transistors for handling high-voltages encountered during flash memory programming and erase operations.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there have been, and continue to be, efforts toward scaling down device dimensions (e.g., at sub-micron levels) on semiconductor wafers. In order to accomplish such high device packing densities, smaller feature sizes and more precise feature shapes are required. This may include the width, thickness and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry, such as corners and edges, of various features.
The requirement of small features with close spacing between adjacent features requires sophisticated manufacturing techniques to ensure that quality and operability of the features are not compromised for the purpose of reducing feature size. Among the many aspects related to improving flash memory device fabrication processing to achieve higher density devices, the ability to form thin films, which are substantially free from impurities and defects, remains critical to the structural integrity of smaller features as well as to the performance of the device with respect to increasing the speed of the device. Even minor impurities or defects present in thin films tend to result in poor device characteristics, thereby reducing the effectiveness of the flash memory device.